The field of the present invention relates to robust polarizing films, such as polyethylene terephthalate (PET) polarizing films, incorporated onto optical-quality plastic parts, such as eyewear, and particularly to improved adhesion of coatings applied to the polarizing films.
As disclosed in the above-identified prior related applications, optical-quality parts may include ophthalmic lenses (semi-finished or finished prescription or non-prescription blanks), lenses, goggles, visors, shields, polarized facemasks or shields, and polarized display devices or windows that require low haze. If polarized, such optical-quality plastic parts may include a number of different types of polarizers on the surface of the optical construct or actually incorporated into the optical construct itself.
Polarizers may include conventionally well-known polyvinylalcohol (PVA) films and the like. As PVA and other typical films are particularly susceptible to heat and other environmental damage, should this type of polarizer film be used on the outside surface of an optical construct, those skilled in the art understand that the polarizer would have to be protected. Such protection is typically in the form of two outside plastic sheets with the polarizer sandwiched thereinbetween, sometimes referred to as a xe2x80x9cwaferxe2x80x9d. In other words, in order to have an optical-quality polarized plastic part where the polarizer is adhered to the outside surface of the optical construct, if the polarizer is a conventional polarizer, the polarizer needs to be in the form of a wafer or the like.
If the polarizer is in the form of a wafer, delamination between the wafer and the construct is of paramount concern, and frequently is the downfall of such conventional optical parts. Alternately, if a strong bond is achieved between the wafer and the construct, further environmental stresses may cause delamination within the wafer itself, separating the needed protective layers from the fragile polarizer. Thus, the bonds between the many layers of the wafer and the construct have usually been the Achilles"" heel of conventionally made optical parts. Moreover, as light must travel through a protective plastic sheet before it reaches the polarizing film, birefringence may occur, resulting in a loss of quality of the polarizing properties when compared to the film by itself. And if a coating is used on the wafer, one skilled in the art must be concerned about the delamination of the coating from the wafer as well.
In an effort to solve such typical problems with conventional polarized optical parts, a more xe2x80x9crobust,xe2x80x9d durable, stable polarizer needed to be discovered to replace the conventionally used polarizers that had so many undesirable properties, such as PVA polarizers. As fully disclosed in their related applications, the inventors discovered that PET had many desirable properties, but this robust material was inert and could not be bonded to constructs using conventionally known techniques. Novel bonding techniques to xe2x80x9cintegrally bondxe2x80x9d (interpenetrated bonding or bonding at the molecular level) the PET polarizing film to the optical construct, as well as an optional optical coating, are fully disclosed in the parent applications.
With respect to optical coatings, as set forth in the parent applications, it may be desirable to overcoat the optical parts for increased physical or optical performance. Common overcoats include scratch or abrasion-resistance layers, anti-reflection coatings, mirrored coatings, and anti-fogging layers. These different coatings may be applied to different surfaces (e.g., a scratch resistant coating on one surface, and a tinted or mirror coating on another), depending on the application.
Such coatings may be applied in the liquid state by roll, spin or dip coating, for example. Depending on the chemistry of the coating solution, the liquid film may be converted to a harder, solid layer by thermal, ultraviolet, infrared or other means of irradiation, reactive initiators or other reactive methods. Vacuum-deposited coatings may be applied as an alternate to the liquid coating, or in addition to cured liquid coatings. Such vacuum coatings may provide additional protection from physical wear, environmental degradation, or further control of the optical properties of the part. For instance, the liquid or vacuum deposited coatings may alter light throughput in a particular energy region to give anti-reflective or reflective (mirror) properties, alter the perceived color of the part, or reduce exposure to emissions such as infrared or ultraviolet emissions.
Similar to the bond between the polarizer film and the optical construct, it is again imperative that excellent adhesion between the polarizer film and the overcoat is achieved to ensure product integrity during use, or during post-processing steps such as shaping, grinding, or edging the part. The parent applications disclose treatments that can be used to improve adhesion to subsequent coatings, including certain chemical modifications of the preferred PET polarizing film surface that lead to improved adhesion of subsequent coatings.
Recognizing the consumer market""s constant demand for better performance from optical parts, the present inventors have improved upon the technology disclosed in the parent applications. More specifically, the present inventors recognized that further enhancement of adhesion between a robust polarizer, such as the PET film, a polyester film or the like, and an optical coating is not only desired but put perhaps critical to preventing failure under extreme conditions such as prolonged exposure to the sun (e.g., leaving your sunglasses on the dashboard) or other such similar abuse.
In an effort to meet the demand for constantly better performance, the present inventors used more aggressive treatments on polarizing films to further enhance the bond between the film and subsequent coatings. In doing so, however, the inventors discovered that more aggressive treatments were often accompanied by physical or chemical damage that deleteriously compromised the required optical quality of either the polarizer and/or the optical and physical properties of the resultant part. The inventors particularly found that more aggressive treatments to the preferred robust (and hence more inert) polarizing films, such as PET films, may be deleterious to their sought-after properties (one skilled in the art understands that the surface treatments proposed in the parent applications, let alone the more aggressive treatments referred to here, may destroy the polarizing properties of the more traditional films such as PVA films). Improved adhesion between film and overcoat, leading to enhanced environmental performance, without compromise of optical or physical properties is therefore desired.
The preferred embodiments relate to methods for improved adhesion of an optical coating to a polarizing film incorporated onto an optical-quality plastic construct comprising treating a surface of the film by mechanical and/or chemical means and applying an optical coating to the treated film for effecting a coated, polarized optical-quality plastic part.
In one aspect of the invention, the treatment may comprise exposing the polarizing film to a caustic solution at a concentration greater than or equal to 10%. In yet another aspect, the treatment may comprise forming grooves having a substantially uniform direction on a surface of the film, dipping the film incorporated onto the construct in a solution comprised of the optical coating, and withdrawing the film in a direction substantially perpendicular to the direction of the grooves.
Another aspect may comprise physically treating a surface of the film by plasma exposure to peen the surface and thereby create a substantially uniform surface roughness, and then chemically treating the substantially uniform surface by plasma exposure.
Such disclosed treatments may be used alone or in combination with another to advantageously effect improved adhesion between the polarizing film and the coating, as well as between subsequent coatings, to thereby enhance environmental performance without compromising the desired optical and physical properties of the film or the resultant optical-quality part.